Brian,
I'm sorry, but it does sound like you are addicted to the diphenhydramine. I couldn't say for sure whether it's a physical or psychological addiction, but, does it really matter? An addiction is an addiction.
Those OTC sleep aids, identical to Benadryl, can backfire on you, too. When I used to take them occasionally, I'd get "kicky legs" the third or fourth night of taking them in a row.
I don't know what 20 times the recommended dose will do to you, but it can't be good, that's for sure.
Have you talked to any doctor about this? I've had insomnia problems for years. My psychiatrist gives me medication to sleep, and changes it when I build up a tolerance to one. I started out taking Restoril, then switched to Prosom, then Ambien, then back to Prosom again. All monitored by the doctor, of course!
I now take 60 mg of Dalmane to help me sleep. It's working wonders. Also, I take 20 mg of Elavil, to help me sleep deeper, because I have Fibromyalgia, which is a whole 'nother story.
A good doctor will prescribe you something, but you have to give it a chance to work, and never, never go over the dose he/she gives you. Prosom is very, very good, for a year or so. Go to a doctor, and explain how you have to take so much OTC meds to sleep. I think Ambien is the only one that is NOT in the benzodiazapine category, you'd have to check on that.
Go to [url="http://www.rxlist.com"]www.rxlist.com[/url] , and look up the medications I've told you about. Ask your doctor about each of them. What works wonders for one person, may not help the next. It's kind of trial and error.
Let me know how you make out, OK? Good luck.